python/clippy/uidhash.py

   1 # SPDX-License-Identifier: GPL-2.0-or-later
   2 # xref unique ID hash calculation
   3 #
   4 # Copyright (C) 2020  David Lamparter for NetDEF, Inc.
   5
   6 import struct
   7 from hashlib import sha256
   8
   9
  10 def bititer(data, bits, startbit=True):
  11     """
  12     just iterate the individual bits out from a bytes object
  13
  14     if startbit is True, an '1' bit is inserted at the very beginning
  15     goes <bits> at a time, starts at LSB.
  16     """
  17     bitavail, v = 0, 0
  18     if startbit and len(data) > 0:
  19         v = data.pop(0)
  20         yield (v & ((1 << bits) - 1)) | (1 << (bits - 1))
  21         bitavail = 9 - bits
  22         v >>= bits - 1
  23
  24     while len(data) > 0:
  25         while bitavail < bits:
  26             v |= data.pop(0) << bitavail
  27             bitavail += 8
  28         yield v & ((1 << bits) - 1)
  29         bitavail -= bits
  30         v >>= bits
  31
  32
  33 def base32c(data):
  34     """
  35     Crockford base32 with extra dashes
  36     """
  37     chs = "0123456789ABCDEFGHJKMNPQRSTVWXYZ"
  38     o = ""
  39     if type(data) == str:
  40         data = [ord(v) for v in data]
  41     else:
  42         data = list(data)
  43     for i, bits in enumerate(bititer(data, 5)):
  44         if i == 5:
  45             o = o + "-"
  46         elif i == 10:
  47             break
  48         o = o + chs[bits]
  49     return o
  50
  51
  52 def uidhash(filename, hashstr, hashu32a, hashu32b):
  53     """
  54     xref Unique ID hash used in FRRouting
  55     """
  56     filename = "/".join(filename.rsplit("/")[-2:])
  57
  58     hdata = filename.encode("UTF-8") + hashstr.encode("UTF-8")
  59     hdata += struct.pack(">II", hashu32a, hashu32b)
  60     i = sha256(hdata).digest()
  61     return base32c(i)